Substrate-induced domain movement, which results in closure of the active site cleft, is an essential part of the catalytic mechanisms of 3- phosphoglycerate kinase. The aim of propagation of ligand-induced conformational changes for this enzyme. The role of the side chain interactions at the interfaces between the adjacent alpha-helices, situated at the domain-domain interface, and their contacts with each domain will be examined using site directed mutagenesis. The location of the 3- phosphoglycerate binding site will also be determined using this approach. The effect of mutations on the catalytic properties of the mutants will be characterized. The structure and stability of mutants will be evaluated using biochemical and physical methods. These studies should contribute to a better understanding of the mechanisms of functionally-important conformational changes in proteins.